In ongoing multibillion-dollar overhaul of the nation’s air traffic control (ATC) system is designed to make commercial aviation more efficient, more environmentally friendly and safer by 2025.

But some white-hat hackers are questioning the safety part. The Next Generation Air Transportation System (NextGen) will rely on Global Positioning Systems (GPS) instead of radar. And so far, several hackers have said they were able to demonstrate the capability to hijack aircraft by spoofing their GPS components.

The Federal Aviation Administration (FAA) has declared that it already has multiple measures to detect fake signals. But it has so far not allowed any independent testing of the system.

The hacking exploits are not new. National Public Radio’s “All Tech Considered” reported last August that Brad Haines, a Canadian computer consultant known online as “RenderMan,” noted that the radio signals aircraft will send out to mark their identity and location under NextGen, called automatic dependent surveillance-broadcast (ADS-B), were both unencrypted and unauthenticated.